Pulse-amplitude modulation (PAM) is an example modulation format where information comprising a message is encoded in the amplitude of a series of pulses comprising the signal. In PAM-4 modulation, 22 (4) discrete pulse amplitudes are available, which are generally equally spaced (i.e., equally spaced in optical power, for optical data transmission). For example, as shown in FIG. 1, a PAM-4 modulation scheme enables pulses to be modulated into one of four discrete amplitudes: [0,0], [0,1], [1,0], or [1,1]. Generally adjacent amplitudes are separated by ⅓ of the largest amplitude (the so called largest bit value).